1. Field of the Invention
This invention relates to a blowout preventer adpated to be connected in series relationship with a line utilized to conduct fluid from an oil well or transmission conduit for the purpose of indicating pressure changes in the conduit.
2. Description of the Prior Art
Blowout preventers have commonly been employed in the small "sense" lines utilized in oil wells and in transmission conduits to feed to a control panel an indication of pressure conditions in the well or conduit. In the event of unusual increase in such fluid pressures, breakage of the sense line or a fire, it is highly desirable that the fluid transmission through the sense line, be interrupted or substantially reduced by a device that is commonly referred to as a blowout preventer. Such blowout preventers also are utilized in a number of similar applications relating to oil field and pipe line applications.
Blowout preventers previously disclosed have normally incorporated valving arrangements which effect the complete shutoff of all fluid flow through the sense line in response to an increase in a biased fluid flow velocity of a preselected magnitude. While such blowout preventers have been adequate from the standpoint of providing protection to the control panel to which the sense line is connected, or preventing large fluid discharge from a broken sense line, they have suffered from the disadvantage that once the blowout preventer has been actuated, some form of manual resetting action has to be performed to restore the blowout preventer to an operative condition. Thus, even though the pressure increase was of a minor duration, prior art blowout preventers would be actuated to their closed position and require resetting.
There is, therefore, a need for a blowout preventer which will permit a volume controlled response to the occurrence of fluid flow surge which will delay the operation of the blowout preventer to its actuated position until a pre-determined small volume of fluid has passed through the device. More importantly, there is a need for a blowout preventer which, except when it is actuated to a closed position by the occurrence of a fire, will not completely close, but only reduce the fluid flow to a safe quantity and yet automatically return to its open position when the monitored fluid flow surge, which caused it to shift to its actuated position, has been eliminated. This allows a pressure sensor to remain active in the instances when there is a fluid flow surge but the sense line has not ruptured.